The present invention relates to a method of after-cooling of the bases of blown out containers as well as to an apparatus for the after-cooling of the bases of blown out containers.
The method of after-cooling of the bases of blown out containers—described here—is based inter alia upon the fact that, after the transfer of the blow moulded containers from a blow moulding machine to a run-out star wheel which follows directly along a conveying direction of the containers to the blow moulding machine, a cooling of the bases of the containers is carried out by means of at least one apparatus for cooling the bases.
In this case the present invention is based inter alia upon the knowledge that in the stretch blow moulding of plastics material containers a residence time in the blow mould can be decisive for cooling the material on a wall of the mould in order to be able to remove dimensionally stable containers from the blow mould. In the course of increasingly higher ejection performances, however, the residence time becomes increasingly shorter. An outer edge layer just in the base region, in which thicker weakly stretched or non-stretched material is always situated, can frequently be cooled only with difficulty. This is due to the fact, inter alia, that a temperature moves outwards from an inner side in the base region, and a (dimensionally stable) outer layer—already present after the blow moulding in a cooling process and therefore already cooled—starts to heat up again and in an insidious manner from the inside for example and/or starts to become deformed in an undesired manner.
In order to prevent an after-heating and/or a subsequent deformation in this way, it has been proposed to set up an after-cooling of the base, in which a base region of a blown out container is cooled once again after leaving the blow moulding machine. In present-day station performances the cooling time in the blow mould can in fact be so low that the impermissible deformation of a base region of the blown out container starts before the start of the after-cooling of the base downstream of the blow moulding machine. In this respect, an undesired subsequent deformation after the blowing out of the base region of the blown out containers can be prevented only with difficulty even with present-day base cooling apparatus.
In this respect, it is an aim inter alia of the present invention to indicate possibilities for letting the cooling of the bases of the containers start before undesired subsequent deformation in this way starts. Such a problem of the undesired subsequent deformation, however, has hitherto been solved only in an inadequate manner in the prior art. Only methods have been proposed in the prior art therefore which inter alia are directed towards more temperature already being dissipated in the blow moulding machine in the region of the blow moulding wheel by way of the base of the blown out containers or having ready blow moulding air in the blow moulding wheel flow from container to container in a manner similar to air recycling, but this has the result of an increased consumption of air.
In this respect, it is an object of the present invention to prevent the problems of an undesired subsequent deformation of the bases as specified above and thus to indicate a method of after-cooling the bases of blown out containers which on the one hand is inexpensive and at the same time allows high clock-time speeds in this case and at the same time subsequent deformation of the bases of blown out containers is prevented.